1. Field of the Invention
The present invention relates to a face detection method and a face detection device for detecting face images from digital images, as well as a program therefor.
2. Description of the Related Art
Techniques such as checking color distribution in a human face area contained in a snapshot taken with a digital camera to correct the skin color of the face, or recognizing a person in digital images taken with a digital video camera of a monitoring system have conventionally been conducted. In such cases, it is necessary to detect a face area that corresponds to a human face in a digital image, and therefore, various methods for detecting images containing faces (face images) in digital images have been proposed.
In one method, for example, in order to detect a face image in an image subjected to detection, partial images are cut out at different positions in the image subjected to detection, and determination is made on each partial image as to whether or not it is the face image. Techniques for determining whether or not a certain partial image is a face image include, for example, a technique using template matching, or a technique using a classifier module that have learned features of faces through a machine learning process (see, for example, “Fast Omni-Directional Face Detection”, Shihong LAO et al., Meeting on Image Recognition and Understanding, pp. II271-II276, July 2004, and U.S. Patent Application Publication No. 20050100195). For this discrimination carried out in these techniques, it is common to use a technique in which an indicator value that indicates a probability of a partial image being a face image is calculated based on an image pattern of the partial image, and if the indicator value exceeds a predetermined threshold value, the partial image is determined to be the face image.
However, in the face detection method, such as those described above using the discrimination technique where determination is made on the indicator values based on the image patterns using a threshold value, if a non-face image pattern that happens to raise the indicator value is present in the image subjected to detection, the non-face image may falsely be detected as a face image.